1. Field of the Invention
This invention relates generally to cable television receivers. More specifically, it pertains to a setback decoder which automatically detects when a scrambled signal is input to a receiver and provides a descrambled output signal to the receiver without requiring any control messages between the decoder and the receiver.
2. Description of Related Art
A typical CATV subscriber installation includes a settop descrambler which is connected between the CATV service provider and the subscriber's television or video cassette recorder (VCR). The descrambler includes a tuner, for tuning the descrambler to a selected CATV channel, and a descrambling module, for providing descrambling of scrambled premium channels that the subscriber is authorized to view. A descrambled video signal is output from the descrambler to the television or VCR on a predetermined carrier frequency, typically corresponding to television channels 3 or 4.
Since the descrambler typically provides a single channel output to the television, many of the built-in functions of the television may become inoperative. For example, the "picture-in-picture" feature requires dual tuners for simultaneous receipt of video signals on two television channels. Since descramblers provide only a single output, the "picture-in-picture" feature becomes inoperative. Additionally, subscribers are often frustrated by the need for multiple remote controllers, one for controlling the descrambler, a second for controlling the television set, and possibly a third for the VCR.
To eliminate the need for a separate tuner within the descrambler, manufacturers have offered televisions with broadband tuners which are capable of accessing the entire CATV frequency spectrum. However, these televisions do not include descrambling capabilities.
Most recently, cable-ready receivers are being developed which receive a radio frequency (RF) CATV input signal and provide an intermediate frequency (IF) output to an associated descrambler. These receivers require the use of a complicated protocol and signaling arrangement between the receiver and the descrambler in order to effectively detect and descramble scrambled CATV input signals viewing by a subscriber. Although the control signaling between the receiver and the descrambler provides full functionality of the receiver while descrambling the desired CATV premium channel, this complex arrangement is costly and difficult to manufacture.
Accordingly, there exists a need for a simple receiver and descrambler arrangement which provides descrambling of scrambled CATV input signals.